Habitat Structural Complexity Research Articles

FAUNA DE FORMIGAS EM ÁREAS DE PRESERVAÇÃO PERMANENTE DE USINA HIDROELÉTRICA

Áreas de preservação permanente contribuem para a recuperação de ambientes impactados e Formicidae representa um grupo potencialmente bioindicador, utilizado para descrever a complexidade estrutural de habitat. Assim, neste contexto, este estudo objetivou caracterizar a diversidade das assembleias de formigas que ocorrem em sítios com diferentes históricos de uso do solo na APP do reservatório da UHE Foz do Chapecó, bem como avaliar a similaridade das assembleias de formigas segundo os sítios amostrados. A amostragem foi realizada no mês de janeiro de 2017 em cinco sítios, três em Santa Catarina e dois no Rio Grande do Sul. Foram utilizados pitfall, guarda-chuva entomológico, isca de sardinha, isca de glicose e coleta manual. As assembleias foram caracterizadas e comparadas através da riqueza, abundância, diversidade de Shannon-Weaver (H’), Equitabilidade (J’) e estimativas de riqueza (Chao 1). Ao todo foram amostradas 101 espécies. A média das estimativas indicou que a riqueza pode ser 86,7% maior que a amostrada, enquanto os parâmetros de diversidade indicaram diferenças entre as assembleias. Os índices de diversidade mostraram divergência de 39,7% entre as assembleias com maior e menor diversidade. A riqueza observada neste estudo reitera o potencial de utilização das formigas como bioindicadoras do estado de conservação ambiental, acrescenta informações importantes sobre a riqueza e a ocorrência de formigas para a região e apresenta, sobretudo, um inventário das espécies de formigas presentes em uma área de APP, em processo de regeneração, que poderá servir de parâmetro para avaliações subsequentes.

Reduced competition may allow generalist species to benefit from habitat homogenization

Abstract Complex environments support high biodiversity and diverse microhabitat availability, which may reduce the intensity of competition among species. Both natural and anthropogenic disturbances reduce the structural complexity of habitats, leading to homogenization. High abundances of common, generalist species in disturbed habitats may be driven by reduced competition from specialists in similar habitats. We quantified habitat availability for and utilization of three co‐occurring arboreal geckos (Australian native house geckos [Gehyra dubia], northern velvet geckos [Oedura castelnaui] and eastern spiny‐tailed geckos [Strophurus williamsi]) in four replicated grazing regimes in an experimental grazing trial in north‐east Queensland, Australia. Native house geckos were most abundant in heavily grazed habitats, whereas the two other species rarely co‐occurred (either with each other or with native house geckos). Geckos displayed resource partitioning of habitat features, such as tree species and structural characteristics. We found evidence of interspecific competition among gecko species, in which native house geckos shifted their habitat selection in the presence of velvet geckos. In the absence of other geckos, native house geckos preferred rough, peeling bark and dead trees, yet in the presence of velvet geckos, native house geckos shifted away from dead trees, and used more structurally complex trees, probably due to high niche overlap with velvet geckos. Native house geckos were more resistant to the negative effects of livestock grazing than either velvet or spiny‐tailed geckos. In the absence of other species, native house geckos used a wider range of microhabitats. Synthesis and applications. Species assemblages are often the results of multiple or complex factors, including predation pressure, habitat availability or competitive interactions. The homogenizing effects on habitat structure caused by livestock grazing reduce diversity and suitability for microhabitat specialists. Reduced competition can therefore promote the abundance of microhabitat generalist species, such as Australian native house geckos, suggesting that livestock grazing leads to homogenization and simplification of habitat structure, which ultimately leads to changes in species composition through reduced competition. Understanding species’ responses to disturbance, and more broadly, habitat complexity, is crucial for maintaining or increasing biological diversity in anthropogenically modified landscapes.

Ecological restoration modifies the value of biodiversity indicators in resident boreal forest birds

A wide range of different biodiversity indicators have been identified in different biomes and types of environments. However, we currently lack a clear understanding under which circumstances proposed biodiversity indicators are valid indicators and when they are not. Here we conducted a large-scale restoration experiment by emulating natural disturbances through prescribed burning and gap-cutting. From this experiment data of resident forest birds was used to, (1) identify biodiversity indicators in the middle and northern boreal zone, (2) test the effect of forest restoration practices on biodiversity indicators and (3) explore the patterns when biodiversity indicator analyses are performed across a wider range of forest types including both restored and unrestored sites. Additionally, to understand the occurrence of species we correlated their occurrence with local habitat structures across different forest types. We found that both the three-toed woodpecker (Picoides tridactylus) and Siberian jay (Perisoreus infaustus) were important biodiversity indicators for the middle/northern boreal zone. The occurrence of these species can generally be used to identify species rich areas across different forest types. However, the three-toed woodpecker, the best indicator for unrestored forest, lost its indicator value after prescribed burning; in these stands the goldcrest (Regulus regulus) was the best biodiversity indicator. Based on habitat associations, we suggest that biodiversity indicators in boreal forest not only indicate high species richness but also structural habitat complexity. Our results draw attention to the fact that one must be careful about using previously identified biodiversity indicators in ecosystems subjected to ecological restoration.

Assessing mesophotic coral ecosystems inside and outside a Caribbean marine protected area.

Widespread shallow coral reef loss has led to calls for more holistic approaches to coral reef management, requiring inclusion of ecosystems interacting with shallow coral reefs in management plans. Yet, almost all current reef management is biased towards shallow reefs, and overlooks that coral reefs extend beyond shallow waters to mesophotic coral ecosystems (MCEs; 30–150 m). We present the first detailed quantitative characterization of MCEs off Cozumel, Mexico, on the northern Mesoamerican Reef in the Mexican Caribbean, and provide insights into their general state. We documented MCE biodiversity, and assessed whether MCEs adjacent to a major town and port, where coastal development has caused shallow reef damage, have similar benthic and fish communities to MCEs within a National Park. Our results show that overall MCE communities are similar regardless of protection, though some taxa-specific differences exist in benthic communities between sites within the MPA and areas outside. Regardless of protection and location, and in contrast to shallow reefs, all observed Cozumel MCEs were continuous reefs with the main structural habitat complexity provided by calcareous macroalgae, sponges, gorgonians and black corals. Hard corals were present on MCEs, although at low abundance. We found that 42.5% of fish species recorded on Cozumel could be found on both shallow reefs and MCEs, including 39.6% of commercially valuable fish species. These results suggest that MCEs could play an important role in supporting fish populations. However, regardless of protection and depth, we found few large-body fishes (greater than 500 mm), which were nearly absent at all studied sites. Cozumel MCEs contain diverse benthic and fish assemblages, including commercially valuable fisheries species and ecosystem engineers, such as black corals. Because of their inherent biodiversity and identified threats, MCEs should be incorporated into shallow-reef-focused Cozumel National Park management plan.

Habitat complexity effects on diversity and abundance differ with latitude: an experimental study over 20 degrees.

Habitat complexity is accepted as a general mechanism for increasing the abundance and diversity of communities. However, the circumstances under which complexity has the strongest effects are not clear. Over 20 degrees of Australia's east coast, we tested whether the effects of within-site structural habitat complexity on the diversity and community structure of sessile marine invertebrates was consistent over a latitudinal gradient where environmental conditions and species composition vary. We used experimental arrays with varied structural treatments to detect whether community cover, species richness, diversity and community composition (β-diversity) changed with increasing complexity. Community response to complexity varied over latitude due to differences in species richness and community development. Increased complexity had the greatest positive effects on community cover and species richness at higher latitudes where recruitment and growth were low. At lower latitudes, community cover and species richness were higher overall and did not vary substantially between complexity treatments. Latitudinal variation in within-treatment β-diversity relative to complexity further suggest divergent community responses. At higher latitudes, increased similarity in more complex treatments suggests community dominance of successful taxonomic groups. Despite limited effects on species richness and community cover at lower latitudes, β-diversity was higher in more complex treatments, signifying potential positive effects of increased complexity at these sites. These results demonstrate the context-dependency of complexity effects in response to variation in species richness and community development and should be taken into consideration to help direct conservation and restoration efforts.

The influence of different deep-sea coral habitats on sediment macrofaunal community structure and function.

Deep-sea corals can create a highly complex, three-dimensional structure that facilitates sediment accumulation and influences adjacent sediment environments through altered hydrodynamic regimes. Infaunal communities adjacent to different coral types, including reef-building scleractinian corals and individual colonies of octocorals, are known to exhibit higher macrofaunal densities and distinct community structure when compared to non-coral soft-sediment communities. However, the coral types have different morphologies, which may modify the adjacent sediment communities in discrete ways. Here we address: (1) how infaunal communities and their associated sediment geochemistry compare among deep-sea coral types (Lophelia pertusa, Madrepora oculata, and octocorals) and (2) do infaunal communities adjacent to coral habitats exhibit typical regional and depth-related patterns observed in the Gulf of Mexico (GOM). Sediment push cores were collected to assess diversity, composition, numerical abundance, and functional traits of macrofauna (>300 µm) across 450 kilometers in the GOM at depths ranging from 263–1,095 m. Macrofaunal density was highest in L. pertusa habitats, but similar between M. oculata and octocorals habitats. Density overall exhibited a unimodal relationship with depth, with maximum densities between 600 and 800 m. Diversity and evenness were highest in octocoral habitats; however, there was no relationship between diversity and depth. Infaunal assemblages and functional traits differed among coral habitats, with L. pertusa habitats the most distinct from both M. oculata and octocorals. These patterns could relate to differences in sediment geochemistry as L. pertusa habitats contained high organic carbon content but low proportions of mud compared to both M. oculata and octocoral habitats. Distance-based linear modeling revealed depth, mud content, and organic carbon as the primary factors in driving coral infaunal community structure, while geographic location (longitude) was the primary factor in functional trait composition, highlighting both the location and ecological differences of L. pertusa habitats from other coral habitats. Enhanced habitat structural complexity associated with L. pertusa and differences in localized hydrodynamic flow may contribute to the dissimilarities in the communities found among the coral types. Our results suggest a decoupling for infaunal coral communities from the typical depth-related density and diversity patterns present throughout soft-sediment habitats in the GOM, highlighting the importance of deep-sea corals in structuring unique communities in the nearby benthos.

Integrating distribution models and habitat classification maps into marine protected area planning

Effective conservation planning requires biotic data across an entire region. In data-poor ecosystems conservation planning is informed by using environmental surrogates (e.g. temperature) predominantly in two ways: to develop habitat classification schemes (1) or develop species distribution models (2). We test the utility of both approaches for conservation planning of marine ecosystems, and rank environmental surrogates, such as depth and distance from shore, according to their power to predict the distribution and abundance of biotic species. Specifically, we compared a habitat classification scheme; based on coarse levels of habitat types derived from depth and distance from shore; against species distribution models, which predict fish abundance and prevalence as a function of environmental surrogates (depth, distance from shore, latitude, reef area, zoning, and several metrics of habitat structural complexity). We consistently set conservation target levels to 21% of each conservation feature, following global standards and a sensitivity analyses. Thus when running scenarios to protect fish species we aimed to protect at least 21% of each species, and when running scenarios of habitat classes, we aimed to protect at least 21% of each habitat class. We found that when aiming to protect 21% of the chosen conservation targets, distribution models protected 21% of the predicted abundance/occurrence of all modelled species and functional groups, but did not protect most habitats. Contrastingly, using a habitat classification scheme protected 21% of all habitat types and 34% of all species and functional groups, but required protecting three times more area. Thus, using only distribution models as targets in data-poor ecosystems could be a risky conservation planning strategy. Ultimately the best conservation outcomes were achieved by incorporating local knowledge to synthesize the conservation outcomes of both scenarios.

Quercus suber forest and Pinus plantations show different post-fire resilience in Mediterranean north-western Africa

In the African rim of the Western Mediterranean Basin, cork oak forests and pine plantations coexist. Under similar fire regimes, cork oak forest is more resilient in terms of habitat structure (canopy, understory, and complexity of vegetation strata) than pine plantation. By contrast, both woodland types show similar resilience in plant species composition. Resilience in habitat structure varies between the two woodland types because of the resprouting and seeding strategies of cork oak and pine species, respectively. These differences can be relevant for the conservation of biodiversity of forested ecosystems in a future scenario of increased fire frequency and scale in the Mediterranean basin. Wildfires have major impacts on ecosystems globally. In fire-prone regions, plant species have developed adaptive traits (resprouting and seeding) to survive and persist due to long evolutionary coexistence with fire. In the African rim of the Western Mediterranean Basin, cork oak forest and pine plantation are the most frequently burnt woodlands. Both species have different strategies to respond fire: cork oak is a resprouter while pines are mostly seeders. We have examined the hypothesis that pine plantations are less resilient in habitat structure (canopy, understory, diversity of vegetation strata) and plant composition than cork oak woodlands. The habitat structure and plant species composition were measured in 30 burnt and 30 unburnt 700-m transects at 12 burnt sites from north-western Africa, where the two forest types can coexist. Habitat structure and plant species composition were compared between burnt and unburnt transects from cork oak and pine plantation woodlands with generalized linear mixed models and general linear models. The results showed significant interaction effect of fire and forest type, since cork oak forest was more resilient to fire than was pine plantation in habitat structure. By contrast, both forest types were resilient to fire in the composition of the plant communities, i.e., plant composition prior to fire did not change afterwards. The higher structural resilience of cork oak forest compared to pine plantation is related to the resprouting and seeding strategies, respectively, of the dominant tree species. Differences in the responses to fire need to be considered in conservation planning for the maintenance of the Mediterranean biodiversity in a future scenario of changes in fire regime.

Accounting for habitat structural complexity improves the assessment of performance in no-take marine reserves

Seascape variability may confound assessments on the effectiveness of no-take marine reserves (NTMRs) in conserving biodiversity. In most cases baseline data are lacking, resulting in evaluations of NTMR effectiveness being Control Impact (CI) assessments. Even with independent replicate areas among management zones, this approach can make it difficult to detect zone effects if seascape attributes, such as habitat structural complexity varies among experimental areas. To determine the importance of structural complexity in evaluations of NTMR effectiveness we performed assessments on the abundance of a targeted fish, yellowtail kingfish (Seriola lalandi), in the Lord Howe Island Marine Park (LHIMP). We compared assessments which did and did not account for structural complexity, quantified using high resolution multibeam bathymetry. Despite almost 3 times more S. lalandi in NTMRs, the traditional CI assessment explained only 3% of the variation in the abundance of S. lalandi and revealed no clear effect of protection. Incorporating structural complexity into the assessment increased the deviance explained to 65% and uncovered an important interaction between zone and structural complexity. Greater abundances of S. lalandi were detected in NTMRs compared to fished zones but only on highly complex reefs. By accounting for structural complexity, we demonstrate that the precision and accuracy of NTMR assessments can be improved, leading to a better understanding of ecological change in response to this conservation strategy. Consequently, where marine park zones vary greatly in structural complexity, we strongly advocate for quantifying and accounting for such variability in assessments of NTMR performance.

Environmental drivers of fish spatial distribution and activity in a reservoir with water level fluctuations

The aquatic ecosystem structuration in human influenced environment, is closely dependent of the associated uses, which are generally fluctuant. We conducted an extended field monitoring on a reservoir under water level fluctuations (WLF), in order to study the responses of fish fauna to changes in environmental conditions. The study design was based on a monitoring of fish behaviour by telemetry in a reservoir with a particular attention to the littoral zone because of its front line position during WLF. The results of this study, which was conducted on the Bariousses reservoir, located on the Vézère river (Corrèze, France), are summarized in this article. The study revealed that WLF induced a temporal variability in the littoral zone surface. In addition, we observed a gradual decline in structural complexity of littoral habitats with a tendency towards homogenisation (dominance of fine substrates and absence of vegetation) in relation with the drop in water level. Behavioural individual responses of pikeperch, perch and pike were highly variable in relation to environmental fluctuations. Temperature and photoperiod were the two main parameters controlling fish activity and spatial distribution. Water level affected part of fish assemblage: some individuals were more mobile and left the littoral zone when inshore habitats were less complex (low water level).

Effects of pond structural complexity on the reproduction of Physalaemus ephippifer (Anura, Leptodactylidae)

Abstract Habitat structure is a factor that strongly affects the distribution of organisms. Habitats with high structural complexity provide a high number of microhabitats, allowing the coexistence of species with different behavioral, ecological and physiological requirements. We analyzed the effects of structural complexity of ponds on the number of males and foam nests of Physalaemus ephippifer, and the substrates to which individuals attach their foam nests. We sampled 41 ponds and recorded the number of individuals of P. ephippifer and environmental data (type of vegetation in, adjacent and around the pond; type of bottom substrate in the pond) to measure the degree of structural complexity of the ponds through an index ranging between 0 and 1. We found a positive influence of pond structural complexity on mean number of calling males, but not on number of foam nests. We found most foam nests attached to gramineans and herbaceous plants. Vegetation is an important component of habitats with high complexity, providing refuges for adults and tadpoles. The index was an efficient tool to measure habitat structural complexity, and may be used in further studies with other species.

Eco-engineering of modified shorelines recovers wrack subsidies

Wrack (stranded phyto-detritus) from terrestrial and marine sources is an important source of carbon and nutrients for many intertidal habitats. In urbanised estuaries, seawalls may act as a barrier to the transport of wrack between terrestrial and marine habitats and, where they reduce the width and habitat complexity of the intertidal zone, negatively impact on wrack accumulation and retention on estuarine shorelines. We assessed differences in the accumulation of wrack between natural (sandy beach, rocky reef and rockpools) and armoured stretches of shoreline, and the efficacy of eco-engineering interventions (man-made rockpools and planted saltmarshes) in enhancing the accumulation and retention of wrack. Surveys conducted at 4 sites in Kogarah Bay, New South Wales, Australia, on 3 dates during autumn-winter 2016 revealed that on natural shorelines most wrack accumulated at the high intertidal mark. Placement of seawalls restricted wrack accumulation to the low intertidal zone, in front of the seawall. The cover of wrack was significantly less in the low intertidal zone in front of seawalls than either the high or low tidal elevations of the natural sandy beaches and rockpools. The man-made rockpools in the low tidal zone had higher cover and biomass of marine and terrestrial wrack than the low intertidal zone of the seawalls, and both these and the planted saltmarshes also supported the accumulation of wrack at the mid intertidal elevation. Experimental deployments of marked seagrass wrack revealed that the eco-engineered habitats enhanced wrack retention over a 7 day period compared with the seawalls. However, the artificial rockpools also retaining more wrack than the equivalent natural habitat. Our results suggest that the structural complexity of eco-engineered habitats can be effective at trapping and retaining wrack, with potential flow-on effects to benthic assemblages through increased food and shelter resources. When designing eco-engineering interventions for modified shorelines, scientists and managers should consider not only their impacts on biodiversity but also on key ecosystem functions.

Habitat structural complexity metrics improve predictions of fish abundance and distribution

Habitat structural complexity influences biotic diversity and abundance, but its influence on marine ecosystems has not been widely addressed. Recent advances in computer vision and robotics allow quantification of structural complexity at higher‐resolutions than previously achieved. This provides an important opportunity to determine the ecological role of habitat structural complexity in marine ecosystems. We used high‐resolution three‐dimensional (3D) maps to test multiple structural complexity metrics, depth and benthic biota as surrogates of fish assemblages across hundreds of meters on subtropical reefs. Non‐parametric multivariate statistics were used to determine the relationship between these surrogates and the entire fish assemblage. Fish were divided into functional groups, which were used to further investigate the relationship between surrogates and fish abundance using generalized linear models. Fish community composition and abundance were strongly related to habitat complexity metrics, benthic biota and depth. Surface rugosity and its variance had a significant positive influence on the abundance of piscivores and sediment infauna predators, and a negative effect on the abundance of predators, herbivores, planktivores and cleaners. Final models for fish functional groups explained up to 68% of the variance. The best metrics to explain the variance in fish abundance were benthic biota (25 ±7.5% of variance explained, mean ± SE) and complexity metrics (16 ±6.6%, mean ± SE). Our results show that high‐resolution 3D maps and derived metrics can predict a large percentage of variance in fish abundance and potentially serve as useful surrogates of fish abundance across all functional groups in spatially dynamic reefs.

The effects of habitat complexity on periphyton biomass accumulation and taxonomic structure during colonization

Habitat complexity plays a significant role in biological communities, but its effect on periphyton is still poorly understood. For example, the response of periphyton to changes in habitat relative to colonization time remains to be elucidated. Our hypothesis was that habitat complexity positively affects periphyton biomass, algal diversity, and change in species composition, while the response of periphyton to habitat complexity depends on colonization time. To test this hypothesis, we evaluated periphyton on artificial substrate distinct levels of habitat complexity at the intermediate (15 days) and advanced phases of colonization (30 days). Biomass, species richness, and diversity increased with level of structural complexity, but these attributes present significant difference only at the 15th day of colonization. In contrast, species composition changed with the increase of fractal dimension at both colonization times. Algal community response to distinct levels of structural habitat complexity was most significant at the 15th day of colonization. Our results showed that biomass, adaptive strategies groups, and taxonomic structure in periphyton were affected by habitat complexity, but that response was dependent on colonization time. Therefore, we concluded that colonization time is a factor that should be considered in assessing the effects of habitat complexity on periphyton.

Habitat complexity dampens selection on prey activity level

AbstractConspecific prey individuals often exhibit persistent differences in behavior (i.e., animal personality) and consequently vary in their susceptibility to predation. How this form of selection varies across environmental contexts is essential to predicting ecological and evolutionary dynamics, yet remains currently unresolved. Here, we use three separate predator–prey systems (sea star–snail, wolf spider–cricket, and jumping spider–cricket) to independently examine how habitat structural complexity influences the selection that predators impose on prey behavioral types. Prior to conducting staged predator–prey interaction encounters, we ran prey individuals through multiple behavioral assays to determine their average activity level. We then allowed individual predators to interact with groups of prey in either open or structurally complex habitats and recorded the number and individual identity of prey that were eaten. Habitat complexity had no effect on overall predation rates in any of the three predator–prey systems. Despite this, we detected a pervasive interaction between habitat structure and individual prey activity level in determining individual prey survival. In open habitats, all predators imposed strong selection on prey behavioral types: sea stars preferentially consumed sedentary snails, while spiders preferentially consumed active crickets. Habitat complexity dampened selection within all three systems, equalizing the predation risk that active and sedentary prey faced. These findings suggest a general effect of habitat complexity that reduces the importance of prey activity level in determining individual predation risk. We reason this occurs because activity level (i.e., movement) is paramount in determining risk within open environments, whereas in complex habitats, other behavioral traits (e.g., escape ability to a refuge) may take precedence.

The role of macrophyte structural complexity and water flow velocity in determining the epiphytic macroinvertebrate community composition in a lowland stream

Habitat structural complexity provided by aquatic macrophytes in lowland streams affects the associated epiphytic macroinvertebrate assemblages in both direct (increased microhabitat diversity, refuge against predation) and indirect ways (e.g. current attenuation by physical structures). In a correlative field study carried out in two different years in a Belgian stream, we investigated the effects of the factors macrophyte identity, macrophyte complexity (represented as fractal complexity) and current velocity on the composition of the macroinvertebrate community associated with monospecific macrophyte patches, consisting of plants with differing structural complexity; Sparganium emersum Rehmann (least complex), Potamogeton natans L. (intermediate) and Callitriche obtusangula Le Gall (most complex). In addition to significantly lower within-patch current velocity being observed, vegetation stands consisting of complex macrophytes also harboured significantly richer macroinvertebrate communities than stands of simpler macrophytes. A significant part of the variation in the macroinvertebrate community composition could be explained by plant identity, macrophyte complexity and current velocity. However, it was not possible to determine the relative importance of these three factors, because of their high degree of intercorrelation. Additionally, the explanatory power of these factors was higher under conditions of high current velocity, suggesting a role of macrophyte patches as instream flow refugia for macroinvertebrates.

Cross-scale habitat structure driven by coral species composition on tropical reefs

The availability of habitat structure across spatial scales can determine ecological organization and resilience. However, anthropogenic disturbances are altering the abundance and composition of habitat-forming organisms. How such shifts in the composition of these organisms alter the physical structure of habitats across ecologically important scales remains unclear. At a time of unprecedented coral loss and homogenization of coral assemblages globally, we investigate the inherent structural complexity of taxonomically distinct reefs, across five ecologically relevant scales of measurement (4–64 cm). We show that structural complexity was influenced by coral species composition, and was not a simple function of coral cover on the studied reefs. However, inter-habitat variation in structural complexity changed with scale. Importantly, the scales at which habitat structure was available also varied among habitats. Complexity at the smallest, most vulnerable scale (4 cm) varied the most among habitats, which could have inferences for as much as half of all reef fishes which are small-bodied and refuge dependent for much of their lives. As disturbances continue and species shifts persist, the future of these ecosystems may rely on a greater concern for the composition of habitat-building species and prioritization of particular configurations for protection of maximal cross-scale habitat structural complexity.

Wild dwarf mongooses produce general alert and predator-specific alarm calls

Many species produce alarm calls in response to predator threats. Whilst these can be general alert calls, some are urgency-based, indicating perceived threat level, some are predator-specific, indicating the predator type present, and some encode information about both urgency level and predator type. Predator-specific calls given to a narrow range of stimuli and which elicit a specific, adaptive, response from the receiver are termed functionally referential. Differing escape strategies, habitat structural complexity and sociality may favor the evolution of functionally referential calls. A study of one captive group of dwarf 3 mongooses (Helogale parvula) suggested their alarm calls could transmit information about species, distance and elevation of predators. Using recordings of natural predator encounters, predator presentations and audio playbacks, we investigated the alarm-call system in seven wild dwarf mongoose groups. We recorded 11 different alarm-call types given to nine stimulus categories. Of the five commonly emitted alarm-call types, three appeared to be non-specific and two predator-specific, given to aerial and terrestrial predators respectively. The remaining six call types were rarely produced. Furthermore, aerial alarms were given to a narrower range of stimuli than their terrestrial alarm calls, which were given to both visible terrestrial predators and secondary cues of predators. Unlike other mongoose species, dwarf mongoose seem to use the same alarm-call type for both physically present terrestrial predators and secondary cues of their presence. We argue that detailed knowledge of species’ alarm-call systems under natural conditions can shed light on the evolutionary emergence of different types of alarm calls.

Adaptations to maintain the contributions of small-scale fisheries to food security in the Pacific Islands

In several Pacific Island countries and territories (PICTs), rapid population growth and inadequate management of coastal fish habitats and stocks is causing a gap to emerge between the amount of fish recommended for good nutrition and sustainable harvests from coastal fisheries. The effects of ocean warming and acidification on coral reefs, and the effects of climate change on mangrove and seagrass habitats, are expected to widen this gap. To optimise the contributions of small-scale fisheries to food security in PICTs, adaptations are needed to minimise and fill the gap. Key measures to minimise the gap include community-based approaches to: manage catchment vegetation to reduce sedimentation; maintain the structural complexity of fish habitats; allow landward migration of mangroves as sea level rises; sustain recruitment and production of demersal fish by managing ‘source’ populations; and diversify fishing methods to increase catches of species favoured by climate change. The main adaptions to help fill the gap in fish supply include: transferring some fishing effort from coral reefs to tuna and other large pelagic fish by scaling-up the use of nearshore fish aggregating devices; developing fisheries for small pelagic species; and extending the shelf life of catches by improving post-harvest methods. Modelling the effects of climate change on the distribution of yellowfin tuna, skipjack tuna, wahoo and mahi mahi, indicates that these species are likely to remain abundant enough to implement these adaptations in most PICTs until 2050. We conclude by outlining the policies needed to support the recommended adaptations.

Does habitat structural complexity influence the frequency of extra-pair paternity in birds?

Several studies have suggested that vegetation structural complexity can influence the frequency of extra-pair copulations, especially by reducing mating-guarding efficiency. Here we investigate if habitat structural complexity affects broad patterns of extra-pair paternity (EPP) and extra-pair broods (proportion of nests presenting at least one extra-pair young—EPB), specifically testing the prediction that species living in habitats with denser vegetation would have a higher frequency of EPP or EPB. We reviewed studies reporting EPP and EPB levels and categorized structural complexity of vegetation for the study population into five habitat categories. Using both phylogenetic ANOVA and phylogenetic generalized least squares (PGLS), we found no significant effects in either EPP or EPB rates. Under the mating-guarding point of view, possible explanations for the lack of support are (i) trade-offs between the possibilities for females to escape from male surveillance and the difficulty to encounter neighbor extra-pair males by visual orientation in areas with dense vegetation; (ii) the predominance of passerine birds in most categories of vegetation complexity, which are small and agile, such that even less vegetated areas may allow extra-pair copulation to be concealed; (iii) environmental components other than vegetation, such as rocks and cliffs, also could provide concealment opportunities for extra-pair copulation; and (iv) the performance of predawn forays, when habitat complexity may play a weak role on guarding effectiveness. A macroecological understanding of EPP and EPB is a continuing challenge for understanding variation in avian mating systems. Our results contribute to improving the knowledge of the impact of habitat in sexual selection. Although a vast literature on avian extra-pair paternity (EPP) and its causes exists, the influence of a number of environmental parameters remains poorly addressed. One such parameter is habitat structural complexity. Scattered pieces of evidence from single-species studies have supported the idea that in more complex habitats, i.e., dense vegetation, extra-pair copulation (EPC) is facilitated by concealment opportunities. Here we provide a broad review on studies reporting EPP and EPB (proportion of nests presenting at least one extra-pair young) levels, and we classified study sites into five habitat categories, which were then compared. After controlling for phylogenetic effect, we found no significant effect. Possible explanations for the nonsignificance under a mating-guard perspective can involve trade-offs between the possibilities for females to escape from social surveillance and the difficulty to encounter neighbor extra-pair mates, the availability of habitat components other than vegetation providing concealment for EPC, and the use of strategies such as predawn forays to avoid mate-guarding consequences. Our results further expand the role of habitat in avian sexual selection.